1. Field of the Invention
The invention relates to containers useful for freeze-drying of biological and similar materials after formation of such a material into a frozen shell-like conformation within such containers.
2. Description of the Prior Art
Containers useful for lyophilization of biological samples are well-known in the art. Containers useful for this purpose are typically formed of glass although they may be formed of resinous materials such as are usually referred to as "plastics". Such containers typically have cylindrical sidewalls, a hemispherical bottom portion and an open end which can be capped by apparatus capable of connecting the container to valves disposed externally of a freeze drying chamber and which allow a material within the container to be subjected to vaccum conditions. Containers can also be disposed within the vacuum chambers of lyophilization apparatus such as is produced by thge Virtis Corporation, among others. Various container sizes and shapes can be adapted to use as lyophilization containers including scintillation vials, serum bottles, etc. Materials which are to be lyophilized are often simply poured into a lyophilization container such as is described above and allowed to assume the shape of the container in the manner that a liquid will assume the shape of a container. Freezing of the material within the container then forms a "slug" of frozen material which is relatively thick throughout and requires substantial time for complete lyophilization of the material. Previous techniques have addressed this problem, a common aproach being the use of "shell freezers" which comprise motor-driven rollers onto which a stoppered container containing a material which is to be freeze dried is placed. The motorized roller apparatus is placed within a freezer and activated to cause the container to rotate during the freezing process, the material then freezing into a cylindrical shell on inner surfaces of the container. A relatively thin layer of frozen material can thus be formed within the container, thereby allowing more rapid lyophilization of the material when compared to the simple formation of a frozen, relatively thicker slug within the container.
A difficulty encountered with prior shell freezers is the requirement for the relatively expensive apparatus needed for motorized rotation of the container and the requirement for placing the roller apparatus within a freezing chamber.
Another problem associated with the freezing of materials within typical lyophilization containers, particularly such containers formed of glass and similar materials, is the fact that the materials contain water which expands on freezing to exert pressure against walls of the container. These pressures can be sufficiently great to cause breakage of the container. Breakage is essentially assured in the event that the container is filled or even nearly filled with the material which is to be lyophilized.
Accordingly, a need has long existed for technology which would allow the convenient and inexpensive ability to form frozen "shells" within a lyophilization container, particularly a glass container, so that the frozen material can be frozen in a uniformly thin shell within the container without the danger of breaking the container during freezing of the material within the container. The present invention addresses this long standing need by providing lyophilization containers within which biological and similar materials can be formed into frozen shell-like conformations having substantially uniform thicknesses throughout to facilitate rapid processing of the frozen material.